Protective rain shields alter leaf microclimate and photosynthesis in organic apple production

Summary

Plastic rain shields reduce the leaf and fruit wetness and protect apple trees against major leaf diseases and hail damage. Shielding the trees may reduce incoming radiation, especially in the ultraviolet (UV) region of the light spectrum, and affect the microclimate and photosynthesis. In July of 2014 and June of 2015, we measured the leaf microclimate and photosynthetic performance using chlorophyll fluorescence and gas exchange in the apple cultivar ‘Santana’ grown in three treatments. In one treatment the trees were exposed to natural light and sprayed (control), and in two treatments the trees were unsprayed and shielded with a plastic film not permeable to UV-light (UV-) or a plastic film permeable to UV-light (UV+). The light transmittance was reduced in the shielded treatments, protecting the leaves from high solar irradiance during noon on sunny days, and avoiding afternoon depression of photosynthesis. Due to this, the leaf photosynthetic rates were often higher in the protected trees in comparison to the control trees at similar high light intensities, whereas there were no differences between treatments on cloudy days. The effect of the UV+ film on photosynthesis did not differ from the UV- film, except there was a tendency for higher values accompanied with increased light transmittance of the UV+ film. We conclude that a microclimate with more diffused light maintained the photosynthetic yield, despite a lower light level under the rain shields.